When it comes to preventing costly damage to diesel engine fuel systems, top quality fuel filters and fuel/water separators are smart choices. By removing hard, gritty microscopic particles, water droplets and other contaminants from the fuel, these devices can help prolong engine life, lower maintenance costs and maximize fuel efficiency.
The role of filters
A fuel filter or a fuel/water separator generally consist of an inner perforated media support tube liner, filter cartridge end caps, heat-cured glue, a round metal housing, seals, thread plate, and the filter media.
“This medium or media is the key technology in a filter assembly,” says Matt Stein, liquid filtration product manager for Donaldson Company Inc., a filter manufacturer. “It balances filtering efficiency, capacity and water removal. Different media balance these factors in different ways.”
A fuel filter uses a pleated media pack, such as plant, wood or synthetic fibers, to remove particulate contaminants from fuel flowing from the fuel tank to the fuel injectors. It traps abrasive particles that can damage fuel transfer and injection pumps and injectors by scoring finely-machined surfaces.
Such damage can reduce fuel flow and lead to pitting of precision surfaces. What’s more, by damaging injector nozzles, the abrasive particles can disrupt the fuel spray pattern in the combustion chamber, causing loss of power, difficult starting, reduced fuel economy, and more harmful emissions.
The most efficient of the new engine filters may typically remove more than 98 percent of the particulates larger than 4 microns. (One micron — a millionth of a meter — is 0.00004 inches. The diameter of a human hair is about 70 microns).
A typical fuel/water separator features a hydrophobic media to block damaging water from the fuel as it passes through the pleats. Water flowing at high velocity between highly polished valve seats and through fine nozzle orifices can lead to costly damage. It can cause rust and other chemical corrosion that eats away at finely mated surfaces. Located before any transfer pumps, this type of filter has a water storage sump and drain valve for draining and collecting the water.
Why filters fail
While stopping hard particles is the first job of a diesel fuel filter, it must also resist clogging with natural asphaltenes (sticky tar-like substances dissolved in all diesel fuels except No.1) and the slime from bacteria that live in the interface between the fuel and any water found in the tank.
Asphaltene particles don’t have to plug a fuel/water separator to cause filter efficiency problems. “Once this filter becomes lightly coated with asphaltenes, the engine will continue to run fine, but the filter’s ability to remove free water droplets is reduced, while the ability to remove emulsified water is nearly destroyed,” says Steven Hardison, fuel product manager for the Racor Division of Parker Hannifin Corp.
“Regular filter changes, instead of waiting for loss of engine power, provide cheap insurance against engine trouble and water damage.”
Cold weather can also cause filter clogging when non-winterized fuel gets cloudy with wax crystals, which build up on the filter media surfaces. An electric or coolant heat exchanger will prevent cold-weather problems. Proper fuel handling will avoid many problems associated with water; but even with the best handling, water from moist air will condense inside fuel tanks and become a problem. That why it’s a good idea to have a good fuel/water separator in the fuel system.
The lower the fuel quality, the more problems with filters plugging, “Heat, fuel degradation and aging causes asphaltenes in the fuel to precipitate into larger, sticky molecules that glob together to plug filters,” Hardison says.
Although fuel filters can fail due to loss of structural integrity, usually they stop working because they have done their job. “All diesel fuel filters have a finite life, and fail eventually due to contaminant clogging,” Hardison says. “Lack of timely maintenance and poor fuel quality are the true sources of most perceived failures.
Improving filter technology
Most fuel filters in construction equipment diesel engines use cellulose fibers from various plants and trees to remove hard particles. However, more sophisticated fuel injection systems and increased use of biodiesel are shortening the life of cellulose filters by causing them to plug up faster. As a result, manufacturers are developing more efficient, longer-lasting filters.
One way to increase filter efficiency is to add synthetic fibers, like glass or fine-spun polyesters. These fibers are much smaller in diameter than cellulose fibers. Wood fibers, for example, may have a diameter of 40 microns, while some synthetic fibers may be no larger than about 0.5 microns in diameter. Hard particles in fuel become trapped in the spaces between the fibers. The fibers themselves also catch and hold the particles. Thus, the smaller diameters of synthetic fibers allow manufacturers to fit more fibers into a given space to capture more particles.
This higher efficiency, however, comes at a much higher cost, Hardison notes. “Filters with synthetic media may cost two to three times as much as cellulose filters.”
Adding more layers of filter media can also boost efficiency. “Some really high-tech filters may have five or six layers of media, each with a different job,” Hardison says. “One may repel water, another resists plugging by asphaltenes, others remove particles only of a given size, while the final layer polishes the fuel.
Evaluating your choices
It’s important to follow manufacturer specifications for type of filter and the replacement schedule. Your best bet, notes Hardison, is to buy them from the OEM or a reputable distributor.
One way to gauge filter performance is to count the number of pleats. The more pleats, the better the filtering capability, Hardison notes. When checking fuel/water separators, he suggests looking for enough space between pleats of the filter for water to collect and drop off.
Hardison recommends replacing secondary/final filters with high-quality filters of the same micron rating and function. Also, consider upgrading your fuel system with a primary fuel filter/water separator with a drain if it does not already have one. This is especially important if you use biodiesel.
Most North American fuel and water/separator filter manufacturers test their products according to various SAE methods. These include SAE J1985, which measures how efficiently the filter removes particles; SAE J1488, which indicates the ability of the filter to remove emulsified water; and SAE J1389, which tests how well the filter removes droplets of free water.
Manufacturers, however, usually don’t report results of SAE tests. Instead they’ll describe performance of their filters in other ways. Racor, for example, describes the percentage of water or hard particles of a given size removed by its filters. “If you can’t find any test data at all about a product, that’s a red flag,” Hardison says.
As you prepare for a new work season, it may be worth considering whether your equipment fuel filtration systems are up to the job — and if not, take action.
